Zero and micro gravity operation of certain equipment requires modifications from its conventional configurations. For example, heat can be removed from a fluid stream by using a conventional condensing heat exchanger (condenser). In a 1 times gravity (1g) environment, condensate (water) forms droplets on the chilled condenser and these water droplets drain to the bottom of the condenser. In a micro gravity environment, the condensate must be removed using alternate technologies. Left unchecked, these water droplets could find their way to electronic equipment and cause equipment failure. Thus, water collection and removal processes in certain micro gravity environments (e.g., the cabin of a spacecraft) are facilitated using condensing heat exchangers having hydrophilic coatings. These hydrophilic coatings minimize the formation of water droplets so that the condensate can be collected from the condenser and removed from the air stream using suction provided by a downstream water separator. The condensate water can then be reclaimed for reuse.
To prevent microbial growth within the condensate, some hydrophilic coatings are supplied with a biocide. U.S. Pat. No. 5,305,827 describes one such antimicrobial hydrophilic coating for use with condensers. This particular antimicrobial hydrophilic coating utilizes silver oxide in the form of Ag2O as the biocide. Silver oxide in the hydrophilic coating dissolves in water to produce silver ions in the form of Ag+. These silver ions serve as a biocide and prevent microbial growth in the water.
During use, condensers and their coatings are exposed to contaminants in the air stream in addition to water. Some substances, such as oils, plasticizers, and silicones can contaminate hydrophilic coatings. When hydrophilic coatings become contaminated, they can lose their hydrophilic properties and become hydrophobic. Once a condenser coating loses its hydrophilicity, the collection of water from the condenser is much less efficient, which can lead to water carry-over in the cabin air stream. For coatings that do not contain silver oxide, the coating can generally be heated to high temperatures (about 260° C. to over 540° C.) to burn off or “ash out” the contaminants. Once a sufficient amount of the contaminants have been ashed out, a coating's hydrophilic properties are restored and the coating is again suitable for use. With coatings that contain silver oxide, however, heating the coating to a high temperature can remove the contaminants, but may also irreversibly render the biocide ineffective. Due to the high costs of producing and deploying water-collecting condensers for spacecraft, a need exists for a method for restoring silver oxide (Ag2O)-containing hydrophilic coatings of condensers that does not compromise the biocidal properties of the coating.